1. Field of the Invention
This invention relates generally to the production of reproducible recordings of video or other signals, and more particularly is directed to methods for producing such recordings by optical means.
2. Description of the Prior Art
The disc recording of audio signals is well known, and involves the use of a lacquer disc for the original recording. Such original lacquer disc, usually constituted by an aluminium base plate with a coating of acetate plastic thereon, is placed on a recording turntable which is rotated at a suitably slow standard speed, for example, 331/3, 45 or 78 r.p.m. During such rotation of the lacquer disc, a cutter including an electromechanical transducer and a cutting stylus is driven in the radial direction of the turntable by means of a lead screw so that the cutting stylus cuts a spiral groove in the record. As the spiral groove is being cut, electrical signals corresponding to the audio or sound signals to be recorded are applied to a driving coil of the cutter transducer for effecting corresponding vibrations of the cutting stylus with the result that undulations are formed in the spiral groove to represent the recorded signals. In mass producing phonograph record discs from such original lacquer disc, the latter is metalized and then electroplated, whereupon the plating is separated from the lacquer and reinforced by backing with a solid metal plate to produce the so-called master which is, in turn electroplated. Thereafter, by well known steps, a mother and then a stamper are produced from the master. Stampers containing the audio signals to be recorded in the opposite sides of the final phonograph record are then mounted in the upper and lower jaws of a hydraulic press, and a preform or biscuit of thermoplastic material is placed between the two stampers which are heated and pressed towards each other by closing of the jaws of the press. When an impression of the stampers has been obtained in the thermoplastic material, the stampers are cooled so as to cool and set the resulting plastic phonograph record therebetween. Finally, the jaws of the press are opened and the phonograph record is removed from the press with the modulated grooves in each face of such record corresponding to those in the respective original lacquer disc. In reproducing the audio signls thus recorded the phonograph record disc is placed on a turntable so as to turn at a constant rotational speed corresponding to that at which the recording turntable was rotated during the production of the original lacquer record. A pick-up is made to track the spiral groove in the phonograph record disc by means of a stylus or needle depending from the pick-up, and the undulations in the groove cause vibrations of the stylus or needle with the result that the pick-up transducer generates an output voltage corresponding to the audio signals represented by the undulations in the groove. Such output of the pick-up transducer, after suitable amplification and equalization, may be employed to drive a loudspeaker which provides an audible reproduction of the recorded sound.
It has also been proposed to record video signals on a record disc by a method similar to that described above for the recording of audio signals. If the resulting video record disc has one frame of the video signals recorded in each turn of its spiral groove, it will be necessary, during reproducing of the recorded video signals, to rotate the video record disc at a high speed, for example, 1,800 r.p.m. in the case of NTSC video signals. It will be apparent that, by reason of such high speed rotation of the video record disc, various technical difficulties will be encountered in reproducing the video signals recorded in the spiral groove of the record disc by means of a pick-up or transducer having a stylus which tracks the groove. Even though such technical difficulties involved in the reproducing of the recorded video signals may be overcome, the recording of the video signals by mechanical cutting of the groove in the original or lacquer record, as described above in the case of the recording of audio signals, cannot be effected with the original or lacquer record being rotated at the high speed of 1,800 r.p.m. If the original or lacquer record is rotated at such a high speed, the cutting stylus is burned by the intense heat generated as a result of the friction between the cutting stylus and the original lacquer record and, further, it is extremely difficult to provide the cutting stylus and transducer with the requisite high-frequency characteristics. Therefore, in practice, the recording of video signals by the mechanical cutting of an original lacquer record is carried out with the recording turntable being rotated at a speed which is about 1/20th the rotational speed to be used when reproducing the recorded video signals. Therefore, if a video record disc is to be provided with a playing time of 10 minutes, more than three hours will be required for the recording of the corresponding original lacquer record. Furthermore, if the original lacquer record is rotated at a relatively slow speed during the cutting of the groove therein, that is, during the recording process, video signals cannot be directly applied to the cutting transducer from a television camera or other video signal source, and it is necessary to provide a frequency converter between the signal source and the recording apparatus. Such frequency converter may employ an intermediate recording medium which is driven at a standard high speed during the recording thereon of the video signals from the television camera or other source, and is then driven at a relatively slow speed during the reproducing of the video signals from the intermediate recording medium for feeding to the recording apparatus by which the video signals are recorded as undulations or irregularities in the groove being mechanically cut in the original lacquer record during the relatively slow rotation thereof. Obviously, the long period of time required for the recording of video signals and the need to employ a frequency converter, as aforesaid, are serious disadvantages of the existing method for producing video record discs.